Redox mercury

Potentiometric Titrations. If one wishes to analyze electroactive analytes that are not ions or for which ion-selective electrodes are not available, two problems arise. First, the working electrodes, such as silver, platinum, mercury, etc, are not selective. Second, metallic electrodes may exhibit mixed potentials, which may arise from a variety of causes. For example, silver may exchange electrons with redox couples in solution, sense Ag" via electron exchange with the external circuit, or tarnish to produce pH-sensitive oxide sites or Ag2S sites that are sensitive to sulfide and haUde. On the other... 

Write a balanced redox equation for the reaction of mercury with aqua regia, assuming the products include HgCl/ and N02(g). 

Mediation, and redox reactions in solution, 585 Medical dosage, 371 Mercury... 

FIGURE 11.22 When ammonia is added to a silver chloride precipitate, the precipitate dissolves. However, when ammonia is added to a precipitate of mercury(l) chloride, mercury metal and mercury(ll) ions are formed in a redox reaction and the mass turns gray. Left to right silver chloride in water, silver chloride in aqueous ammonia, mercury(l) chloride in water, and mercury(l) chloride in aqueous ammonia. 

When the area A of the eleetrode/solution interface with a redox system in the solution varies (e.g. when using a streaming mercury electrode), the double layer capacity which is proportional to A, varies too. The corresponding double layer eharging current has to be supplied at open eireuit eonditions by the Faradaic current of the redox reaction. The associated overpotential can be measured with respect to a reference electrode. By measuring the overpotential at different capaeitive eurrent densities (i.e. Faradaic current densities) the current density vs. eleetrode potential relationship can be determined, subsequently kinetic data can be obtained [65Del3]. (Data obtained with this method are labelled OC.)... 

Mercury(II), thallium(III), and lead(IV) are isoelectronic and, as can be seen from the data in Eqs. (19)-(22) (77) the redox potential for thallium is intermediate between those of mercury and lead. Consequently, the relative oxidizing ability of the three metal ions should be in the order Hg(II) <... 

C19-0014. The mercury battery, use of which is being discontinued because of the toxicity of mercury, contains HgO and Zn in contact with basic aqueous solution. The redox products are Hg and ZnO. Determine the oxidation and reduction half-reactions and the overall reaction for these batteries. 

Studies of the electrodeposition of mercury chalcogenides are scarce, primarily because of the difference in electrochemical potentials needed to deposit mercury and the chalcogens. Mercury is a noble metal the standard redox potential for the... 

Fig. 5.6 (Left) Comparison of band energy levels for different II-VI compounds. Note the high-energy levels of ZnSe. Representation is made here for electrodes in contact with 1 M HQO4. The reference is a saturated mercury-mercurous sulfate electrode, denoted as esm (0 V/esm = +0.65 V vs. SHE). (Right) Anodic and cathodic decomposition reactions for ZnSe at their respective potentials (fidp, Fdn) and water redox levels in the electrolytic medium of pH 0. (Adapted from [121])...

The additivity principle was well obeyed on adding the voltammograms of the two redox couples involved even though the initially reduced platinum surface had become covered by a small number of underpotential-deposited mercury monolayers. With an initially anodized platinum disk the catalytic rates were much smaller, although the decrease was less if the Hg(I) solution had been added to the reaction vessel before the Ce(lV) solution. The reason was partial reduction by Hg(l) of the ox-ide/hydroxide layer, so partly converting the surface to the reduced state on which catalysis was greater. 

It is also important to understand how the potential gradient between an electrode and the bulk solution is established and controlled. Because the potential difference between the electrode and the bulk solution is not measurable, a second electrode must be employed. Although in general the potential difference between an electrode and solution cannot be determined, the potential difference between two electrodes in that solution can be determined. If the solution electrode potential difference of one of the electrodes is held constant by maintaining a rapid redox couple such as silver-silver chloride or mercury-mercurous chloride (calomel), then the potential... 

Lalonde JD, Poulain AJ, Amyot M. 2002. The role of mercury redox reactions in snow on snow-to-air mercury transfer. Environ Sci Technol 36 174-178. 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

The present chapter will cover detailed studies of kinetic parameters of several reversible, quasi-reversible, and irreversible reactions accompanied by either single-electron charge transfer or multiple-electrons charge transfer. To evaluate the kinetic parameters for each step of electron charge transfer in any multistep reaction, the suitably developed and modified theory of faradaic rectification will be discussed. The results reported relate to the reactions at redox couple/metal, metal ion/metal, and metal ion/mercury interfaces in the audio and higher frequency ranges. The zero-point method has also been applied to some multiple-electron charge transfer reactions and, wheresoever possible, these results have been incorporated. Other related methods and applications will also be treated. 

This redox couple has been studied in H2S04 and tartaric acid at the dropping mercury interface by Delahay et al.u They only reported the value of a for the reaction. This system is only stable when the concentration of Ti3+ is 10 to 20 times higher than that of Ti4+. The AE / V versus w l/2 plots for this reaction in 1.0 N HC1 are shown in Fig. 10 and the kinetic parameters60 are given in Table 3. The value of a is 0.49 and k°a = 5.56 x 10 4cm/s. The reaction appears to be irreversible. 

See other chlorite salts, mercury compounds, redox compounds... 

Square planar complexes [M(mru)2]3 (M = Rh, Co, mnt = dithiomalonitrile), generated by electroreduction of [M(mnt)2]2, are protonated to form [M(mnt)2I I]2 ", from which dihydrogen is evolved at a mercury electrode at potentials more negative than those of the reversible [M(mnt)2]2 3 redox couple.44... 

One example of a — Hg- linked TTF dimer has been reported [106]. Linear coordination is expected for the mercury atom. Extended Hiickel calculations indicate that the mercury orbitals are essentially not involved in the HOMOs, and thus the two TTF redox groups can be regarded as being completely isolated from each other. The voltammograms confirm these expectations in that both TTF... 

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